1 . Field of the Invention
Flow control devices are commonly employed in a variety of applications, such as balancing heating, venting, and cooling (HVAC) systems and regulating flow through gasoline pump systems. Past attempts at regulating flow originated around the use of restricted orifices within the fluid line and the use of manually adjustable valves. However, these solutions failed to sufficiently overcome the problems associated with varying fluid pressure within the line, and thus, were not capable of accurately regulating flow. To overcome these problems, flow control devices capable of regulating flow and limiting it to a preset maximum despite varying fluid pressures within the line are commonly used.
Flow control devices capable of automatically regulating flow despite varying line pressures differ in design, but generally comprise a casing having a generally hollow interior, a casing inlet, and a casing outlet, a generally hollow piston having a piston inlet and an edge, wherein said piston is slidably mounted within the interior of the casing in a manner such that the edge is cooperable with the casing outlet to control the flow of fluid through the device, and a means, such as a spring, for biasing said casing with said piston. Additional embodiments may have the piston sliding over the casing or have an edge of the casing cooperating with the piston inlet to control, either alone or in combination with the effect of the piston edge cooperating with the casing outlet, the flow of fluid through the device.
Functionally, flow control devices are generally positioned within a line or valve housing and operate via a pressure differential between the upstream portion of the device and the downstream portion of the device. For example, in the common piston and casing design, as fluid flows through the piston inlet, the differential pressure increases across the piston and compresses the biasing means causing the casing outlet to be closed off by the edge of piston. As the casing outlet closes off, the pressure in the interior of the casing increases and, in conjunction with the force of the biasing means, works to equalize with the pressure upstream of the device. As the pressures approach equilibrium, the biasing means actuates the piston upward allowing the fluid outlets to reopen.
Although the prior art has been effective at regulating fluid flow under certain circumstances, the prior art has not been successful at accurately and precisely measuring the actual flow rate through a device in real time. Flow measurements of the type known in the prior art have relied on pressure measurements taken from positions in the fluid flow line upstream and downstream of the line position of the flow control device. While it is possible to calculate the rate of flow of a given fluid through a fixed orifice when the pressures upstream and downstream of the fixed orifice are known, it has not been possible to accurately and precisely calculate the rate of flow in the flow control devices of the prior art as such devices have at least one variable orifice such as, for example, a piston inlet or casing outlet that opens or closes as the piston element slides within the casing of the device. Because a variable orifice prevents the accurate and precise calculation of flow rate based on the pressures upstream and downstream of the orifice, prior art flow control devices have not been capable of real time flow rate measurements. In view of the limitations of the prior art, it has not been previously possible to accurately or precisely verify or adjust the flow rate of a given flow control device.